In an internal combustion engine, particularly, in a 4-cycle internal combustion engine, a valve moving mechanism and spark plugs are provided for the cylinder head. Such a cylinder head structure has been disclosed in JP-A-1-193009 and JP-A-1-280605. According to the cylinder head structure disclosed in JP-A-1-193009, a hydraulic tappet is provided for a rocker shaft to axially support one of the rocker arms, and the other rocker arm is pivotally supported by the hydraulic tappet, thereby simplifying the working of the cylinder head. According to cylinder head structure disclosed in JP-A-1-280605, the forming position of an intake valve and the forming position of an exhaust valve in the width direction perpendicular to the longitudinal direction of the cylinder head are fixed and the cylinder head for the moving valve system is constructed, thereby enabling the outer shape of the cylinder head and the working equipment to be commonly constructed irrespective of the number of intake and exhaust valves and enabling the parts which are used to be also commonly constructed and reducing the costs.
Internal combustion engines are classified into the straight-type, opposed-type, V-type, and the like in accordance with the arrangement of the cylinders. For instance, as shown in FIG. 4, a V-shaped internal combustion engine 102 is constructed in a manner such that first and second cylinder heads 106-1 and 106-2 are mounted on an almost V-shaped cylinder block 104 and first and second cylinder banks 108-1 and 108-2 are arranged in an almost V-shape. One first cam shaft 1101 and one second cam shaft 110-2 are arranged in the first and second cylinder heads 106-1 and 106-2 of the internal combustion engine 102 in the longitudinal direction, respectively. First and second intake valves 112-1 and 112-2 are arranged in the first and second cylinder heads 106-1 and 106-2 on the inner side of the internal combustion engine 102 in the width direction, respectively. First and second exhaust valves 114-1 and 114-2 and first and second spark plugs 116-1 and 116-2 are arranged on the outer edge side of the internal combustion engine 102 in the width direction, respectively. Reference numerals 118-1 and 118-2 denote first and second cylinders; 120-1 and 120-2 first and second intake cams; 122-1 and 122-2 first and second exhaust cams; 124-1 and 124-2 first and second rocker arms; and 126-1 and 126-2 third and fourth rocker arms, respectively.
As shown in FIG. 4, however, the first and second exhaust valves 114-1 and 114-2 and the first and second spark plugs 116-1 and 116-2 are arranged on the outer edge side of the internal combustion engine 102 in the width direction of the first and second cylinder heads 106-1 and 106-2, respectively, so as to be inclined from first and second cylinder center lines 118-1L and 118-2L of the first and second cylinders 118-1 and 118-2. That is, as shown in FIG. 5, the second exhaust valve 114-2 and the second spark plug 116-2 are arranged on the outer edge side of the internal combustion engine 102 in the width direction of the second cylinder head 106-2 in a manner such that a second exhaust valve center line 114-2L and a second spark plug center line 116-2L are inclined from the second cylinder center line 118-2L of the second cylinder 118-2.
Therefore, there is a disadvantage in that the width of the internal combustion engine 102 is enlarged because the first and second exhaust valves 114-1 and 114-2 and the first and second spark plugs 116-1 and 116-2 project from the outer edge side of the internal combustion engine 102. There is also a disadvantage in that the weight of the internal combustion engine 102 is increased, an increase in the size of the engine room of the vehicle is required, and the weight of the vehicle is increased. Since the first and second spark plugs 116-1 and 116-2 are obliquely arranged, there is a problem such that it is difficult to easily attach and detach them. Thus, maintenance efficiency is deteriorated. Further, when an accessory 128 such as a radiator or the like exists on an extension in the spark plug attaching/detaching direction, the attaching/detaching of the first and second spark plugs 116-1 and 116-2 is difficult and the maintenance efficiency is deteriorated. In order to assure the maintenance efficiency of the internal combustion engine 102, the accessory 128 must therefore be located away from the engine. There is consequently a disadvantage in that an enlargement of the engine room is required and the weight of vehicle is increased
In an attempt to solve the above disadvantages, according to the invention, in a cylinder head structure of an internal combustion engine in which first and second cylinder heads are mounted on an almost V-shaped cylinder block and first and second cylinder banks are arranged in an almost V-character shape, wherein a first cam shaft and a second cam shaft are respectively arranged in the longitudinal directions of the first and second cylinder heads of the internal combustion engine, first and second intake valves are respectively arranged on the inner side of the internal combustion engine in the width directions of the first and second cylinder heads, and first and second exhaust valves and first and second spark plugs are respectively arranged on the outer edge side of the internal combustion engine in the width directions of the first and second cylinder heads, the cylinder head structure is characterized in that the first and second cam shafts are respectively arranged so as to be deviated to the inner side of the internal combustion engine in the width directions of the first and second cylinder heads, and the first and second exhaust valves and the first and second spark plugs are respectively arranged so as to be almost parallel to respective center lines of the first and second cylinders.
According to the invention, the first and second cam shafts are respectively arranged so as to be deviated to the inner side of the internal combustion engine in the width directions of the first and second cylinder heads. The first and second exhaust valves and the first and second spark plugs are arranged so as to be almost parallel to the cylinder center lines of the first and second cylinders, respectively. Consequently, the width of the internal combustion engine can be reduced and the spark plugs can be attached/detached from positions over the internal combustion engine on extensions of the cylinder center lines.